


Siren

by NecromanticNoir



Category: Harry Potter - J. K. Rowling
Genre: Anal Sex, Creature Fic, Knotting, M/M, Mating Cycles/In Heat, Oral Sex, Secret Snarry Swap 2017
Language: English
Status: Completed
Published: 2017-12-12
Updated: 2017-12-12
Packaged: 2019-02-09 04:04:19
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 6,986
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12879798
Author URL: https://archiveofourown.org/users/NecromanticNoir/pseuds/NecromanticNoir
Summary: Severus Snape was not one for ‘dating’. It fell to him, then, to capture himself a Mate.





	Siren

**Author's Note:**

> Wishing my Giftee a very Snarry Christmas, I hope that you enjoy this. Hugs to you! Thank you to the Mods for running this again and making us feel all festive and full of Snarry joy.
> 
> Prompt 5 from eriador117: For some reason (potions accident, curse, maybe he's part Veela or something) Harry goes into heat and it's up to Snape to keep him from committing any indiscretions--at least, keep him from committing any indiscretions with anyone else.

Severus Snape drew out the thin tendril of black smoke between his fingers.

Like a spinner, he pinched the smoky thread and, with his dark eyes flashing, silently affixed it to another. Weaving; spinning his net. Wherever the thread came undone, he cursed under his breath, muttering an incantation. Light slipped from string to string. A web of neurones crackling and pulsating with dark magic.

The edges of the net, he wove to be strong, teasing out the smoke from a flickering black candle. Intent on his work, stopping only to wipe the dripping sweat from his brow and nose, he worked until the candle burned down, then lit another. He always had been domineered by his obsessions. Sometimes, he remembered to eat.

His supper that night was plain. A bowl of lamb stew, cold. A small piece of bread. He read as he ate, turning the pages in between mouthfuls.

‘The Siren is almost exclusively found near water, in unstable areas prone to shipwrecks or other disasters. However, it has been found that the Siren is able to exist away from water. Be warned: the penchant for luring men to their deaths does not diminish in these cases. Sirens have been known to lure men to fall from bridges, be stampeded by a herd of cattle, and become lost in forestland and swamps, to name but a few. Water is a prominent theme, but without it, the Siren still triumphs.

‘Thought of as exclusively female, in fact the Siren can be male also; thus sharing the traits for unnatural beauty and the ability to lure their victims in - for whatever purpose they might design.

‘There are few known examples of a traveller meeting a Siren whence did not come almost immediate death. Men are not known to mate with Sirens on the whole, and scant tales exist of the man lured in to share a Siren’s ‘heat’. Heat is known, like Omegas, Veelas, Vanteera and Harpies, as a period of intense breeding ranging from three days (Harpies), one week (Omegas and Veela) and up to two weeks (the Siren). The need to mate is all-consuming, and it falls within the realm of possibility that a man might happen upon a Siren during that time. Woe betide those that do.’

Snape closed his book. His eye burned like banked coals.

*

Severus Snape was not one for ‘dating’. This much had been obvious for his entire life. Now, at forty-five, living in isolation, dead to all the world, he had the time to ponder such things. Isolation should have been bliss after all he had suffered; it was, however, boredom and suffocation. A man with his quick mind required a challenge, he needed to be frustrated and angered and aroused. He also knew too well his predisposition towards obsession; a human would not understand, would expect Snape to date, and to simper and flirt and tease, and to have distance. At forty-five, he knew his own nature. He wanted to own, and to consume, and to be broken by someone.

Or, something.

It fell to him, then, to capture himself a mate. Of the magical creatures that could mate with humans, the Siren appeared the most ethereally beautiful - and the most deadly.

Snape was hooked from the moment that he had opened the book.

He had no experience with life’s gentler emotions - a Veela would expect to be worshipped - and he had no desire to be eaten alive by a Harpy. The Siren, however, never actually killed with their own hands, and had a voracious sexual appetite. Snape shivered.

It occurred to him at a quarter of three one morning, as he lay there bare-chested, staring at the ceiling, that a creature gripped by desire for two weeks might feel let down if Snape could not… perform as often as needed. He sat up, pulled a nightshirt on, and started to prowl his bookcases.

He spent three days brewing (and testing) sexual enhancement potions, and settled finally, instead of one which gave him a burst of desire that left him exhausted, on a potion to mirror his sexual desires to his partner’s. It gave him bouts of nausea, but lasted about three hours, which he considered a success.

Thoughts of having a dark-haired Siren to share his bed filled his nights with fevered dreams. He had already decided that he wanted a male: a dormant lifelong desire which he might as well fulfil now. He was beholden to no-one.

-

The night before his first hunt, he could not sleep.

He checked the net five times, and then again.

He checked the bars of the cage he had made, the floor of which was piled high with feathers and straw for the creature’s nest. He could not find anything in the books which alluded to where the Siren slept, so he had taken inspiration from the Veela and the Vanteera, who nested like birds, and the Harpy, who also made a nest (admittedly of the bones of its victims). He had a stock of raw meat and fish, and charms made of seashells strung inside the cage.

He had his potion.

All was ready.

-

The rain lashed against his skin. His sodden hair hung limp about his face, sticking to his neck. Water trickled down the back of his collar. He scraped his sodden hair back out of his eyes.

Three days he had been out here in the wilds, sustained only by magic and the tiny animals that he had managed to trap. He would starve - no - he would freeze to death before he found the Siren. His boots were full of water which no charm would dry. His cloak was a wet rag, clinging to his body.

The only thing still dry was the net.

He was on his knees when he heard it. The Siren song.

It was unearthly - Snape’s breath caught in his throat. The song filled him up with ambrosial sunlight; blasted through him like ice water; crippled him instantly like a fever.

He clenched his fingers in the dirt, gritted his teeth, squeezed his eyes shut. It was an onslaught of the most exquisite pleasure he had ever felt - so much so that it stole his breath, constricted his heart -

He stumbled after the sound. He had never heard the song so close before and he wanted it - oh how he wanted it!

It felt as if he walked for days after it, stumbling over rocky ground and through mud so deep that it seemed to welcome him in. Gasping, dazed, he realised that he had wandered into a bog. It was sucking him down like a toothless mouth. Mud, like gums, squirmed at his legs, turned them heavier than lead. Vines crawled towards him and their red flowers opened mouths full of spines, sinking themselves into his arms and shoulders.

He was gasping, weak as water; a groan of white light erupted from his wand, and the mud desiccated and turned to powder.

As he lay panting and bleeding on the wet grass, the Siren song sounded again.

-

The rocks beneath his boots crumbled at each step - had he not been taught the skill of flight by the Dark Lord, he would surely have plummeted down onto the sharp rocks below.

As it was, he lost his footing on a slippery stone, and gashed his leg open on rock as barbed as glass. He ripped off the hem of his robe to bind up the wound, pulling it tight in his teeth and wincing at the pain.

He was close to the sea. The wind howled like a banshee, but it could not drown out the Siren song.

It was then that he saw the creature - sitting on a rock with its knees pulled up to its chest, staring out to sea.

A male.

He was surprised to see that it wore a soaked red hoodie, and - jeans? There could be no doubt that this was the Siren, however - the song came again, and almost brought him to his knees.

It seemed that the creature had not noticed him in the gale.

With the last of his strength, he threw his hand-woven net at the Siren.

Instantly, the creature started to rise, and the once-bewitching song turned so foul in his ears that he had to clutch at his own head in case his brains exploded.

The creature could not escape his clutches, however - despite the rain, the dark net opened out in midair like the breath of a maleficent dragon. It enveloped the Siren in a cocoon, and the creature crumbled to its knees - as did Snape, his strength finally giving out. His last coherent sight was the Siren kicking and punching fruitlessly at the net, before he slumped heavily onto the chalk ground, and knew no more.

-

He came back to himself at twilight - the chill in the air and in his lungs was a rude awakening. Groaning, he felt his back crack as he tried to sit up. The blood on his leg had encrusted - when he moved, it strained the wound partly open, and he hissed.

Then his eyes fell upon the net. The creature was still in it, lying motionless, the slim chest rising and falling as though in sleep.

Snape sat bolt upright, his dark eyes flashing. His heart - the long dormant, desiccated organ - roared awake, triumph pumping blood through his veins again as he stood over the creature. “My own, my creature,” he sneered, inflated with pride and arrogance. “You must be as beautiful as your song - shall we find out?”

Levitating his parcel, he walked the long road back to his cottage. He resisted the temptation to slit the net open and take a peek, as it prolonged his anticipation. He already knew that the creature would be magnificent.

He deposited it in the cage, and the slim body sank into the bundle of feathers. He would keep it in the net until it awoke.

He sealed the cage with a spell, collected up bandages, thin twine, needles, knives and three pastes of his own designing - and a bottle of firewhisky - and settled down on the stone floor to tend to his wounds, and to wait.

-

Some hours later, his ripped and sodden robe discarded, Snape slumped against the wall in his shirtsleeves. The neck of his shirt gaped open and his hair hung in tangles. He had his book on magical creatures, for reading again about the Siren, but had discarded it in favour of staring at the creature and brooding, and imagining wild sex. He had kicked off his boots, and was about to take another swig from the whisky bottle, when the Siren began to stir.

The net was designed so that sound could permeate from outside in, but not the other way around, to limit the power of the song.

He approached the bars, eyes glinting in the darkness.

“Can you understand me?” he slurred. The creature stilled. “Ah, you can. I do not intend to harm you.” The Siren tried to sit up. “Be still! I will remove the net in a moment. You are,” he whetted his lips, “mine now.”

He gripped the bars in both hands. “Did you hear me? I have you bound - mastered - and you will look only to me to satisfy your… appetites. I will provide for you, and in return I expect your supplication and deference. Should you try to harm me, you will sorely regret it.” He took a breath, and a sip from the bottle. “In return, I will fuck you as hard as you want me to, not only during your heats - whenever you desire it.” The creature was still. “You are in a cage - once you have proven your respect, you may share my bed. Do you have a name? Once I remove the net, you may tell it to me. You may refer to me as ‘Master Snape’, if you can speak.”

He drew out his wand from his pocket. “I am going to release you now.”

A whispered spell, and the net melted away - and Snape was left staring into the frightened (and stunningly beautiful) green eyes of Harry Potter.

His breath caught in his throat - choking, he staggered back. The bottle smashed on the flagstones. “You!”

Potter’s mouth worked, but no sound came out. Snape brandished his wand, snarling - “You little fucker! What is this? How have you tricked me?”

“I haven’t!” Potter gasped out. He was as thin as the last time Snape had seen him - older, yes, and with a sharp jaw and full, luscious mouth that Snape was sure he would have remembered. “Snape, you’re alive!”

“So it would seem,” Snape sneered. “You cannot expect me to believe that you are a Siren?” Potter was wildly handsome, it was true, but surely a song as intoxicating had not come from -

Potter blinked, and the song rippled off him in waves.

“Stop!” Snape screeched.

The melody faded.

He stumbled; leant his shoulder against the wall for support, breathing hard. “How,” he choked on the words, “did this happen?”

“I turned twenty-one,” Potter said, gravely. “It was awful. Turns out someone in my ancestry was… what I am now.”

“How is this not widely reported?” Snape demanded.

“Because the nature of the Siren is to lure men to their deaths,” Potter snapped. “So I did. And then I had to leave - I’m a danger to everybody! Why on earth do you want a Siren to mate with?”

“Do not mention that,” Snape hissed. He slumped back against the wall, sinking to the ground.

All these months of work -

“I can’t believe you’re alive! How did you do it? Does anyone else know? Where are we now, is this your house?”

“None of your business, no, Scotland, and yes,” Snape sneered. “I can’t believe I caught you! You! Fucking shit! Ever accessible to men, are you?”

“No! I’ve never even shared a heat, actually - I was sat on that cliff top trying to work out what to do with my life -”

Snape’s head snapped up. “What? If you are not lying to me, you became a Siren four years ago!”

Potter sighed. “I isolated myself after… the incident happened. I haven’t seen anybody else since.”

“So what do you do during your heats?” Snape sneered. “I suppose those aren’t all that the books make them out to be, just my luck,” he added darkly.

Potter blinked at him. “What do the books say?”

“That it is comparable to an inferno of blistering sexual desire,” Snape said, morose.

Potter shrugged. “That does kind of sum it up. It’s not much fun on your own. Do you have any food?”

“What do you eat, apart from cock?” Snape snapped.

Potter coloured. “I told you, I’ve never -”

Snape struggled to his feet. “Pheasant or fish. Do you take it raw?”

Potter nodded, shuffling and looking a little embarrassed. “Fish, please.” His gaze fell.

Snape nodded gruffly and turned to go - but then, the Siren song sounded again.

Weak at the knees, he grabbed hold of the doorframe for support. Turning back to Potter with a snarl, he beheld the young man, sitting in his cage with his knees crossed. The look on his beautiful face was… coy. As though he were testing out his power, and the outcome fascinated him.

Angered at being dangled on a string, Snape fixed Potter with a dark glare. “Are you trying to get yourself into deep trouble, Potter?” he whispered.

Potter’s lips quirked; the green eyes sparkled. “I just wanted some fish, Professor.”

“You’re trying to get a good arse-fucking, you smug little shit,” Snape spat.

Potter bit his lip; squirmed a little. “I… I wouldn’t be safe for you.”

“YOU wouldn’t be safe for ME?” Snape choked out.

“It’s in my nature to try and lure men to their deaths,” Potter reminded him.

“It is in my nature to fuck up everything that I associate with,” Snape sneered. “You dare try.” He turned back to the door - but the Siren song blasted again, and he stumbled, hitting his knees on the way down.

“Shit!” He heard Potter gasp, and scramble to his feet. When Snape looked, the young man was gripping the bars of his cage, trembling faintly as he gazed down at Snape, his eyes huge. “Don’t go,” Potter whispered.

Snape rolled onto his back and closed his eyes, teeth gritted. His breathing slowed. Eyes still shut, he said: “I understand. You think that you are still in school. You think there is a code of conduct that I must follow, such as not punching you, not eviscerating you, and not ripping off your clothes and sticking my tongue up your tight little arsehole.”

Potter - unbearable little slut that he was - whimpered. “Are you even gay?”

“Are you?” Snape sneered, opening one eye. “Are you sure I’m enough to please you?”

“I can, er, sort that,” Potter mumbled.

Snape rolled onto his side, looking at him. “What?”

“Um, well I need a mate who, er…” Potter winced, “who can knot me. And is, um, pretty large. And can do it to me as many times, erm, during my heat as I need…”

“If you were an Omega, only a born Alpha would do,” Snape snapped.

“I know,” Potter said, “but they’re prized possessions, Omegas. I’m… more of a liability. I have to make what I want.”

Snape knew the feeling. “And how do you make these… adjustments?” he sneered.

Potter stared at the floor. “I don’t know. I imagined I just… willed it. I haven’t had anyone to try it out on yet -”

“Experiment on, you mean,” Snape barked.

“Worried it’ll hurt?” Harry snapped back - then he paled. “Oh God, what if I do hurt someone?”

Snape snorted. “I imagine that anyone willing to let you try to enlarge their cock would have to accept the consequences.”

“You’re the one that captured a Siren knowing that you didn’t have the equipment for it,” Potter smirked.

Snape got to his feet, looking down his nose at Potter. “I was prepared, if you must know, with a temporary solution. I shall bring your fish.”

-

Outside the door, Snape sank into the nearest chair. Potter! The little shit was like a disease - more infectious and enthralling than James Potter’s brat had any right to be… Had those green eyes always glowed thus? And that body always been so tight and - Snape shuddered. God.

He had caught a beautiful Siren. A Siren who was of age, and abandoned, and desperately in need of mating.

But it was Potter!

‘You are thinking like his Professor,’ his brain supplied, ‘which you no longer are, and have not been in over seven years.’

He brought the fish to Potter with a speculative glare, which Potter ignored. The way that he ate the fish was ravenous - and exquisite. As blood dripped down Potter’s chin, Snape stood in the doorway and contemplated him. “Have you tried to mate with anything non-human, since your ‘change’?"

Potter’s eyes widened. “Non-human? Like what?”

Snape shrugged. “You said that you had abstained from the company of humans.”

“No,” Potter said, curtly. “I haven’t fucked any wolves, or beasts, or centaurs.”

“How did the man die?” Snape asked, folding his arms.

There was a silence.

“I lured him to his death,” Potter spat.

“Yes, I know,” Snape sighed, “but how exactly did you do it?”

Potter set aside his fish skeleton, stricken, as though he had lost his appetite. “God, you Slytherins want all the gory details, don’t you!”

“As I am currently at risk of your… enchantments, I think I should be prepared.”

Potter was silent for a long time. “I lured him in front of the Knight Bus.”

“How did you know that it would be passing?” Snape scoffed.

“That’s the scariest thing - I just knew,” Potter mumbled. “I have an instinct for ways that, if circumstances went wrong, people would die. Bad luck - I know just how to make you be in the wrong place at the wrong time.”

“How would you kill me right now, then?” Snape demanded.

Potter shook his head. “It’s not about that - it’s about knowing when the time is, er, right. It’s as natural as breathing - if I can get you to stand in one spot, I know that the roof will fall just there in a few minutes. It’s never planned too far in advance. I just know how to make you move one step to the right and into the path of a dragon, when it’s about to happen. How could I stay in my flat in Diagon Alley knowing that I was like that?”

“So you’ve been roaming the wilds of Scotland ever since, spending weeks on end masturbating in the bushes?” Snape sneered.

Potter flushed. “What are you intending on doing with me now? I heard what you said, you wanted a Siren to be your possession, to mate with it and fuck it and have it belong to you. Why not find a human?”

“I imagined a Siren to be less complicated,” Snape said darkly.

Potter grinned. “Boy, were you wrong! Are you intending to release me, then?”

Snape paused. He should just dump Potter back out into the wilds and begin the hunt again. “What do you wish me to do?” he asked, his lip curling.

Potter blinked at him. Then, to Snape’s surprise, he looked suddenly coy again. “That depends how noble and honourable you are, as a contemporary of my parents.”

“As a former Death Eater, spy, murderer and fugitive, you mean?” Snape bared his teeth.

Potter shivered, a small smile playing about his lips. Then a strange look came over his face, like a shadow, or an eclipse of the moon. “Oh shit,” he whispered. The smile fell away.

“What?” Snape demanded. He watched in consternation as Potter stood, then sat, then tried to nest in the feathers, then stood again, then scratched at his arms and neck, sweat breaking out on his brow. “What are you doing?” Snape snarled, disquieted.

“It’s… it’s coming on, I - I can’t remember when the last one was, maybe it’s due -”

Snape gasped. “Only you, Potter, would inveigle your way into my home and my hospitality - and then go into heat!” he snarled.

“Inv - what?” Potter gasped. “You kidnapped me! And told me you wanted to fuck me really hard and what a bad man you are - what am I supposed to do? I can’t control it! It just… overtakes everything and I can’t -” He thumped the bars in frustration. “Are you just going to sit here and watch me wank myself raw for two weeks?”

Snape opened his mouth to say something scathing - but then the Siren call started: low this time, like a chant, undulating and pulsing. He gripped his hands into fists. “What is that?”

“It’s heat, it’s the sound it makes,” Potter gritted out, bent against the bars as though he had a crippling stomach ache. “Fuck! Help me!”

“How dare you,” Snape growled. “You will stop this, now.”

“I can’t!” Potter groaned. Snape could see the sweat beading on his brow. Potter unzipped his jacket. “It’s awfully bloody hot in here.”

“No it isn’t,” Snape snapped, but Potter was shrugging his red hoodie off his shoulders. His thin t-shirt was sticking to his taut body, wet from the rain. Snape’s mouth fell open in spite of himself.

Potter started fanning his neck and chest. Leaning against the bars, he parted his legs, toeing off his shoes. He plucked at his t-shirt, itching from foot to foot. “Can I have some water?”

“No,” Snape spat. “Stop this behaviour.”

Potter pulled off his shirt, balled it up, and threw it across the room. His chest glistened. His nipples were tight and pink, his belly was flat, and a trail of luscious dark hair licked its way down into the waistband of his jeans.

Snape’s mouth went dry.

“You have to help me. Do you have anything I can use?” Potter growled.

“Use?” Snape demanded.

“I… God!” Potter scowled. “To put in my arse!” Snape choked. “Either that or get over here yourself! It’s awful - I need to mate so badly, Snape, you can’t send me away! What will I do? Lost in the wilds on my own, desperate to mate!”

“I am not equipped,” Snape muttered, but he stepped closer - close enough to be within arm’s reach -

“I’ll fix that,” Potter breathed - and then his palm reached out, cupping Snape’s crotch. The effect was like lightning, wild and fresh. Snape cried out as though electrocuted, seizing the bars of Potter’s cage as the Siren’s metamorphic power surged through him. At first, he felt only the ache, but then his groin started to throb, and he gritted his teeth, Potter’s wide green eyes gazing into his. Then there was pain, and he looked down sharply, “What are you doing to it?”

“Bigger.” Potter bit his lip. “Need it to knot too -”

Snape leant his forehead against the bars and grimaced, eyes screwing shut. Teeth bared, he tried to breathe deeply through his nose. When he opened his eyes, he realised that Potter’s face was right there. The boy reached through the bars and cupped his jaw with his other hand, and pressed a soft kiss to his mouth.

“It’s ok,” Potter whispered, soothing him. “Just a few more moments, you’re so strong, it’ll be worth it, we’ll mate for life -”

Sweat slid down his temple; his hands clenched tight -

Then Potter released him.

He sank to the floor, head spinning, and Potter knelt too, gazing down at him with hunger flickering in his wild eyes. The Siren song was different now - it flowed in his veins, like the aftershocks of an orgasm. He leant his face against the cooling slate and breathed through the storm.

“My Mate.” The word was a soft exhalation full of wonder. A prayer. Potter petted at his hair, his hip, his shoulder, anything he could reach.

Snape lifted his head. With trembling hands, he scrabbled at his belt and to undo the zip - the flesh underneath felt so tender as he pushed a hand inside.

“Let me see,” Potter whined.

Snape drew out his prick - carefully - and winced again as he gawped at it, engorged and fat, leaking obscenely, pulsing against his stomach.

Potter’s mouth fell open. “Oh yes,” he growled.

With a thirsty look on his face and his eyes flashing, Potter stepped right through the bars as though they were air, as though they were butter, and straddled him, mindful of his tender prick. The boy drew a finger softly down its length, lips curling upwards. “God yes.”

“You little beast -” Snape snarled.

“I ought to wait - I ought to lure you to me,” Potter whispered. “But I don’t think I need to. I think I already did it.”

“You certainly did something,” Snape murmured, pushing his hips up into the juncture of Potter’s thighs, jolting the young man a bit. “It’ll never fit in you at that size.”

Potter looked down at him, green eyes glowing, and Snape had the unsettling feeling of being a fly caught in a spider’s web. “Oh, it will. _Professor_.”

“I expect,” he rasped out, “that you’ll be expecting me to instruct you in this, too.”

“You couldn’t teach me anything even when you were my teacher, sir,” Potter grinned. “Help me; keep me out of trouble.” He slid a hand round and gripped Snape’s prick.

“Do you think I am at your mercy?” Snape hissed.

“The Siren song seems to bring you to your knees,” Potter smirked. “God, I can’t even fit my hand around it.”

Snape raised his hands to Potter’s hips. “You’ll be the one on your knees,” he snarled.

They stared at each other.

Then, Potter was curling over, palms clasping Snape’s face, and Snape was leaning up -

Mouths meeting halfway, and oh God the Siren song seem to flow from Potter’s lips. Wet, and sweet, like nectar, honey in his veins. The touch of the creature’s tongue against his was divine. Potter’s fingers were in his hair; the boy was shaking. Snape scratched the small of Potter’s back softly - his other hand gripped a firm hold of Potter’s arse.

Potter gasped into Snape’s mouth. “Need to Mate,” he whispered, his breath hot. His eyes drifted towards the pile of feathers. “In there.”

He sat up. Snape leant up on his elbows and watched as Potter fumbled hurriedly with the buckle of his own belt. The boy - no, young man - stood, dropping his trousers and toeing off his socks as he stumbled towards the nest. “No time to tidy it up,” he growled, as Snape snatched at him, pinning him to the floor with his larger body.

“Where do you think you are going? Don’t you need preparation?” Snape growled in his ear, sinking his hands inside Potter’s red boxers and grabbing palmfuls of fresh, round arse, hard enough to leave handprints.

Potter barked out a laugh. “Look at it,” he gasped. Snape rose onto his knees and yanked down Potter’s underwear - the boy pushed his hips up, parted his knees, and pulled his own buttocks apart. The softly twitching hole was wide and damp, and leaking onto the back of Potter’s underwear. He could see inside it, the tunnel of pink spongy flesh -

“What the devil is this?” he hissed - and pushed a finger inside it. Potter made a desperate sound and arched his back. Snape twisted, facing Potter’s feet, and buried his face in the crease of Potter’s arse, his nose in the boy’s balls. His sharp tongue slid easily inside - the taste was even sweeter here - he spread his large hands over Potter’s buttocks and pushed his tongue as far inside as it would go.

Potter howled. “Oh shit, shit!” He wriggled out of his boxers and spread his legs wide, twisting and grabbing at Snape’s head, trying to push his face harder against his hot skin.

“Right,” Snape snarled, as he pulled back and gasped for breath. He turned, hauled Potter up onto all fours, and nudged the tip of his prick against Potter’s pink flesh.

“Fuck my arse, fuck my arse, fuck it, fuck it - fuck it!” Potter screamed - on the last exhalation, Snape had shoved inside him. Potter screeched in delight - Snape smacked his arse hard as he pulled out, then pushed back in. To his amazement, the boy’s needy pink prick, stiff as iron, instantly squirted out reams of white come. Potter shuddered, and howled, and it was atrocious, Potter’s hole stretched so tight around his cock, large as a beater’s bat. He pushed two fingers of each hand in alongside his cock, and stretched it out more -

“Oh my hole, oh my fucking hole,” Potter wailed, pushing back; trying to impale himself further, his own smaller pink cock still rock-hard.

Snape pulled completely out, bit Potter on the arse, and shoved back in again. Potter screeched. As he shoved in, Potter exhaled, as though there was not enough room inside him. Snape draped his chest over the boy’s sweaty back and ground his hips hard into Potter’s arse.

“You’re still wearing clothes,” Potter moaned. Snape’s greasy hair hung in his face as he turned his neck - Snape realised that the eyes had changed to red now; a wild red to match Potter’s over-bitten lips. He bit them himself, then released Potter’s lower lip when the boy groaned.

“Your eyes,” he snarled.

“Mating,” Potter gasped. “Someone told me they’ll turn red when I’m mating.”

Snape pulled partway out, then forced his blunt cock back in. There was an obscene slurp. His arm came up round Potter’s throat; his hands clawed at Potter’s damp flesh and thrust in more rhythmically.

“Can’t believe… haven’t… done this… before!” Potter wailed. “Need… more… men!”

“You will have no such thing!” Snape snarled, gripping Potter’s jaw with his sharp fingers. “I captured you - you will stay here.”

Potter sucked one of the fingers into his mouth. “Yes, yes,” he whispered, eyes drifting closed.

Snape sneered. Suddenly he pulled out of Potter and hauled the boy around, pushing his huge slimy prick into the boy’s face. “Look what you did to it, you little slut,” he growled.

Potter stared at it - and came. His cock spurted again; streams of white come shot up across his belly. Potter instantly opened his mouth and lavished his tongue along Snape’s shaft, even as his own cock still spurted, his eyes closed blissfully. His mouth was just wide enough to stretch around the head, and he choked and gagged as Snape’s hips jerked.

Gasping, drooling, Potter looked up at him with his red eyes - Snape instantly pushed him backwards, his legs in the air, and dived on top of him. Feathers flew and stuck to Potter’s wet skin, as he shoved his prick into Potter’s ravenous hole over and over. Potter’s fingers slid up under his shirt, scratching furrows into his back. The boy was a wet, sloppy mess: mouth red, eyes watering, hair damp and sticking to his face, covered in his own come, tight nipples leaking a clear fluid that tasted sweet when Snape sank his mouth over one. Any hard thrust seemed to cause Potter to orgasm, and there was no diminishing the amount of creamy spunk that splattered over his firm chest.

He fucked Potter hard into the floor until his back ached and his knees ached and his elbows ached and all he could taste was Potter’s come. There was no sating the little beast; it just went on and on. Snape dimly had the confusion that his own orgasm seemed to be taking an eternity; there was nothing as hot as Potter’s filthy body under him, wet and raw and screeching with joy and biting his neck and scratching his back to shit. Potter’s kisses were a never-ending source of nectar; licking his skin was a mouthful of warm sunshine. He had the boy bent in half, legs alternating between being jolted in the air and wrapped around Snape’s waist. Finally, his knees protested too much against the slate floor - he stopped, panting, and Potter’s eyes snapped open, red like a furnace -

“NO!” Potter’s otherworldly voice howled, and Snape was rolled onto his back, feathers flying as Potter scrambled to sit on his cock.

He sat down on it so hard that Snape’s toes curled, but all Potter did was smile, eyes drifting closed. He reached down and tore Snape’s shirt open, palms spreading freely over Snape’s hairy chest and up his neck, fingers slipping into his mouth. Snape bit them, and Potter started to ride him hard, slamming himself down onto Snape’s prick over and over. Snape threw back his head, gripped Potter’s hips, and shoved upwards to meet him. The Siren song sounded, so he did it again, and again, until Potter was being jolted and slammed into and abused, and crying with delight. His orgasm splattered come over Snape’s face and into his hair.

Snape realised later that his stamina potion with just three hours’ duration would have been woefully inadequate.

Potter was bent over his worktable by that point, screaming and thrashing as Snape held his shoulders down and pistoned hard into his arse, balls slapping against the flesh. Snape, exhausted and pissed off, reached round and slapped the boy in the face. “How much fucking do you need?” he panted, and Potter only laughed and sucked at his fingers and pushed himself back onto Snape’s cock, and orgasmed again.

“Ahhh, make it so I can’t walk,” Potter growled. “Fuck me!”

“You’re not going to be able to use this hole for anything else,” Snape snarled back. “It’s too fucking stretched, it’s like a mouth -” He pumped hard into Potter, watching the firm skin of the young man’s butt ripple with his thrusts, hearing Potter squeal as his breath was jolted from his lungs.

“Shit, knot me, knot me,” Potter howled, and Snape realised that this command was what he had been waiting for.

Crying out, he pulled Potter’s hips back to meet him with every hard thrust, even has he felt the base of his cock begin to swell. Potter’s hole stretched white and red around it, popping in and out - until one final thrust popped it in and it sealed, draining Snape of the most powerful orgasm of his life. Over and over, he felt himself pulse into Potter as he cried out into Potter’s neck, pulling his dark hair back sharply, making Potter squeal and cry and orgasm as the knot pulsed inside him.

“You’re a predator,” Potter whispered, and came again. Snape caught it in his hand and smeared it over Potter’s chest.

“So are you, little beast, enjoying being mounted so much,” Snape snarled.

When the knot finally subsided, and his prick slipped out, there was a slurping noise as his come slopped out of Potter’s hole and dripped onto the floor. He realised, exhausted, that he was still hard. Leant over Potter, watching the slender back rise and fall as Potter panted, he realised that it was not over. Potter turned in his arms, lay back on the table, glistening with his own come, and hooked his ankles around Snape’s back.

“Mate with me more,” he croaked.

Snape shoved in again. The slurping sound this time was louder - and made Potter come instantly. Snape gripped his hand behind the boy’s head and lifted it sharply so that the come shot straight into his mouth - Potter moaned, and came again, his tongue pink and raw, and kissed his come against Snape’s tongue.

-

Dimly, in the days that followed, he remembered passing out and being revived by Potter with water, and meat, and fruit - and then being straddled again and Potter bouncing hard on his cock and screeching. He remembered having Potter standing up, with Potter pressed into the wall, scrabbling at the stones. He remembered carrying Potter around, clinging to him like a limpet, while Snape fucked him. He remembered lying on his back, with Potter atop him, his back to Snape’s chest, fucking himself on Snape’s cock and coming all over himself. The times when he would knot, and lie there still inside Potter, with Potter trembling with delight around him, were but a momentary lull in the storm. It seemed as though Potter’s lure would never let him go.

-

Fifteen days passed.

Snape came to one morning in the wild nest of feathers. His head ached. Potter lay quiet in his embrace, his birds-nest hair sticking up in all directions, his skin flushed and soft.

Potter opened his eyes - back to green again - and smiled. “You look fucking wrecked, Snape.”

Snape snarled. “You’re hardly a virtuous maiden yourself.” He squeezed Potter’s bruised arse and the boy snorted, mouthing at a bite mark blossoming on Snape’s shoulder. The boy’s back was littered with bites and bruises - Snape’s own back smarted. He shifted a little. “This place stinks of spunk and sweat, and whatever fluid it is that leaks out of your filthy arse and nipples -”

“That you like, that you kept sucking out of me,” Potter interrupted.

“Am I stuck with this monstrosity forever now?” Snape complained, looking down at his cock, draped weakly against his thigh.

“You like it,” Potter grinned. “It is monstrous, though,” he added, laying his head happily on Snape’s chest.

“I’ll have to get new trousers,” Snape grumbled.

“You’ll only need to wear them for half the month, I wouldn’t bother,” Potter yawned. “It’ll be in my arse the rest of the time.”

“You’re staying then, are you?” Snape groused. “I need a piss - when was the last time I did that?”

“You did capture me,” Potter reminded him. “Oh - um, don’t get up just yet. There’s a wolf outside - if you go outside to piss, it’ll get you.”

“How do you know that?” Snape demanded.

“It’s been there for a few days,” Potter yawned again. “I thought about sending you out, but then you were mating with me SO well.”

“Yes, please do try to rein in these impulses to send me to my death,” Snape said, sourly. “I can’t believe you considered killing me whilst I was fucking you!”

“It’s my nature,” the Siren said, flinging an arm and a leg over Snape. “Have you got any more fish?”

“No, but if you let me find my wand, I’ll kill the wolf for you,” Snape said, petting Potter’s hair.

“You’re so kind to me,” Potter smiled. “When you get your wand, the sink has been leaking for three days, so if you aren’t careful, you’ll slip and hit your head. Just to warn you.”

“How kind. You’re a menace,” Snape snapped, pulling Potter close, skin on skin, but Potter was already falling asleep.

Stuck as a pillow, Snape noticed his book on magical creatures lying on the floor. He reached for it, careful not to dislodge Potter, and found his bookmark.

‘The need to mate is all-consuming, and it falls within the realm of possibility that a man might happen upon a Siren during that time. Woe betide those that do. The Siren is the only magical creature that fully controls the time at which they mate. Omegas and Veelas are subject to a monthly ‘cycle’, whereas the Siren can bring on a heat at will.’

Snape snapped the book shut and glowered at Potter. He opened his mouth, teeth bared - then paused. Snape looked up at the ceiling, listening for the snuffling of the wolf outside, and wondering how else this beautiful creature in his arms was going to try to do him in. It was incredibly frustrating, and angering, and all-consuming, and Potter would very likely break him in the end.

Snape smirked into the darkness and tightened his hold.

**Author's Note:**

> Please leave a comment here or at [Livejournal](https://snape-potter.livejournal.com/3776678.html), [Insanejournal](http://asylums.insanejournal.com/snape_potter/1711417.html), or [Dreamwidth](https://snape-potter.dreamwidth.org/1022755.html).


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